DE102019219278A1 - Method for determining the camshaft position of a series engine - Google Patents

Abstract

The invention relates to a method for determining the camshaft position of a series engine, with reference measurement values being determined on a reference engine, with a pressure profile with several pressure measurement values being recorded in the inlet and / or outlet tract of the series engine, with an actual camshaft value (NWMod) being determined based on the pressure profile The method is improved in that at least one crankshaft angle (φ_Peak) of a local extreme of the measured pressure values of the series engine is determined, with the actual camshaft value (NWMod) of the series engine depending on the extreme of the reference engine and the determined crankshaft angle (φ_Peak) of the local extreme Pressure readings of the series engine is determined.

Description

The invention relates to a method for determining the camshaft position of a series engine with the features of the preamble of claim 1.

An engine control is driven by a crankshaft via, for example, gear wheels or a control chain to the camshaft. The cams of the camshaft open and close the cylinder inlet and outlet valves via transmission means. A working cycle of the cylinders extends over four cycles, whereby the valves are only actuated once so that the camshaft runs at half the speed of the crankshaft. The lifting movement of the inlet and outlet valves must be carried out at the right time and in the right sequence by means of the camshaft. With a camshaft adjustment, the position of the intake camshaft and the exhaust camshaft in relation to the crankshaft can be changed.

In the prior art, it is known to measure a so-called reference internal combustion engine in all operating states that occur and to store these measured values or model approaches derived therefrom on the engine control unit of a corresponding series internal combustion engine. All identical, series-produced internal combustion engines of the same series are operated with this generated reference data set. A deviation of the actual relative position between the camshaft and the crankshaft on a series internal combustion engine from the reference position leads to the fact that the fresh gas charge actually sucked in deviates from the fresh gas charge determined as a reference. An angular misalignment of individual cams on the camshaft causes the same error pattern as an angular misalignment of the camshaft and crankshaft. The aim is therefore to be able to better adjust the camshaft rotation position of the series intake and exhaust valves.

It is known to apply a position mark to any point on the camshaft or a coupling element or the crankshaft, which position mark is detected by a sensor. As a result, a relative position between the crankshaft and the camshaft can be determined and deviations can be identified. However, only part of the deviation is recognized here, since, for example, a phase angle offset between the individual cams cannot be recognized during assembly or when the tolerances are produced.

From the generic DE 10 2015 209 665 A1 the evaluation of a pressure signal is known. With this method, the valve timing of a series internal combustion engine is identified. Dynamic pressure fluctuations are measured in the intake or exhaust tract of the series internal combustion engine in question, and a crankshaft position feedback signal is also determined. From the measured pressure oscillations and the crankshaft position feedback signal, the phase angles of selected signal frequencies of the measured pressure oscillations are determined with the aid of a Fourier transformation. Based on the determined phase angle and the use of reference phase angles and reference valve timing of the same signal frequency of the pressure oscillations of a reference internal combustion engine and a model function derived therefrom, the camshaft position and thus valve timing of the relevant series internal combustion engine are determined. This state of the art has the disadvantage that it is complex and cannot be implemented in a cost-neutral manner.

The invention is therefore based on the object of improving the method for determining the camshaft position.

This object on which the invention is based is now given by a method having the features of the patent claim 1 solved.

A pressure curve with several pressure measured values in the intake and / or exhaust tract of the series engine is recorded. According to the invention, at least one crankshaft angle of a local extreme of the measured pressure values of the series engine is determined, the actual camshaft value of the series engine being determined as a function of the extreme of the reference engine and the determined crankshaft angle of the local extreme of the measured pressure values of the series engine. The necessary calculations are not complex, which improves the method. The pressure curve is preferably determined at a constant crankshaft speed, but it can also take place when the crankshaft speed rises or falls.

The actual camshaft value NW_mod is determined by multiplying the crankshaft angle φ_Peak of the extreme with a factor f and adding a correction factor NW _Mod = f * φ_Peak + c, the factor f and the correction factor c being determined from the reference measured values. The correction factor can take into account physical parameters that lead to an extreme shift.

It is advantageous that the crankshaft angle of the extreme value takes place as a function of a temperature T of the inlet tract or of the outlet tract and a crankshaft drive speed n. By measuring on the reference engine, the camshaft position is known at a maximum or a minimum of the pressure curve. The position of the maximum can depend on further factors, such as, for example, the speed and the temperature, in particular the temperature of the intake manifold and / or the exhaust gas temperature and / or the temperature of the outlet tract. The corresponding temperature in the inlet tract or in the outlet tract is measured during the process. A correction value c can be determined as a function of the rotational speed and the temperature in order to determine the actual value of the camshaft position using the reference model. This correction value can be specified by a map derived from the measurements on the reference engine.

The correction value is preferably determined by a map c = K (n, T), the map value having been determined in advance from the reference measured values, the map value being dependent on a crankshaft speed n and a temperature T of the inlet and / or outlet tract. Alternatively, the correction factor can be described by several characteristic curves or by at least one mathematical equation, for example a polynomial P (), for example c = P (T, n), c = P (n) or c = P (T).

The camshaft position is preferably determined on cylinders that are in overrun mode. In overrun mode, the camshaft is set to a constant setpoint at a stationary speed. The measurement in overrun mode has the advantage that the extremes known from the reference measured values can be measured more precisely on the series engine, since no fuel combustion takes place in overrun mode and pressure pulsations caused by the combustion are thus avoided.

When the actual camshaft value has settled, the pressure is measured over one camshaft revolution, in particular to a crankshaft angle of 1 °. The pressure profile is now first recorded by recording several measured values in the inlet and / or outlet tract. In particular, an intake manifold pressure in the intake tract and / or an exhaust gas counter pressure in the exhaust tract can be measured. The pressure is measured over at least one camshaft revolution and several pressure measured values are recorded. Such a measurement is preferably carried out several times, which has the advantage that a more robust signal is obtained.

To determine the extreme, a measured value interval of the pressure profile around a crankshaft angle is preferably selected at which the extreme value occurs in the reference model. This makes it easier to find the extreme in the series engine.

Preferably, several extremes are evaluated which are assigned to the movements of different cylinders. For example, the extremes assigned to cylinders 1 and 4 can be evaluated. The extremes are at different crankshaft angles, with a measurement interval being selected for the first cylinder and a measurement interval for the second cylinder. An averaged measured value interval is now formed from the multiple measured value intervals by adding the corresponding measured values of the measuring interval and dividing them by the number of measuring intervals.

The actual camshaft values are then modeled by evaluating the extreme values in the pressure curve. The position of the extreme values is a measure of the actual camshaft angle and this can be determined with the aid of reference data that originate from a reference measurement on a reference engine.

The extremes are determined by means of a signal analysis. An extreme value of the pressure and the associated rotational position can be determined solely from the recorded measured values. However, this extreme value is coarse and imprecise, since the angle information supplied by the measured values alone can be disturbed by high-frequency superimpositions.

The extrema is determined by means of a mathematical equation through a least square estimate of the measured values or the averaged measured values in the measuring interval. The mathematical equation is preferably a polynomial, in particular a polynomial of the second degree. Alternatively, for example, a fourth degree polynomial can be used. The polynomial or the underlying mathematical model can be interpreted at this point as filtering the pressure signal. The angle information is improved in that several measured values are used around the extreme value and are interpolated by the polynomial, in particular a quadratic polynomial, in a model. A plurality of measured values, preferably more than 10 measured values, in particular more than 15 measured values, in particular approximately 20 measured values, are used to determine the coefficients of an in particular quadratic polynomial. For this purpose, a least square estimate is carried out.

The coefficients of the polynomial can be determined by a least square estimate. The extreme value of the polynomial can be calculated by equating the first derivative with 0. The real pressure curve P (φ) is mapped in the area of the extreme value by a polynomial: P (φ) = w0 + w1 * φ + w2 * φ ² by equating the first derivative with “0”, the local extreme value is determined. dP / dφ = 0 + w1 + 2 * W2 φ * from this follows φ _peak = - w1 / (2 * w2). _{The actual camshaft position NW Mod} can be calculated from this value with the above equations.

To determine the coefficients w0 to w2, in one embodiment a least square optimization is carried out, e.g. by a QR decomposition or a Cholesky decomposition. That means a conversion into a linear system of equations. In a preferred embodiment of the implementation of the method, the least square optimization is carried out by means of orthogonal polynomials, which further minimizes the computational effort.

It is advantageous if a mean value of the deviation of the actual camshaft value from the reference value is formed. This allows the extrema to be determined more precisely. The model value or the model value minus the real actual angle of the camshaft is preferably fed to a ring memory. If there are enough values here and the spread of these values is below a threshold, the result is reliable. The mean value from the ring memory is the system's camshaft error.

To determine the actual camshaft value of the intake camshaft, the extreme value is a maximum and the temperature is the intake manifold temperature. The method can also be used to determine the actual value of the exhaust camshaft. Here the extreme value is a minimum and the temperature is the exhaust gas temperature. The minimum value can be determined here for all cylinders.

• 1 in einem schematischen Ablaufdiagramm das Verfahren zur Bestimmung der Nockenwellenlage.

There are now a large number of options for designing and developing the process. Reference is first made to the claims subordinate to claim 1. In the following, a preferred embodiment of the invention is explained in more detail with reference to the drawing and the associated description. In the drawing shows:

• 1 the method for determining the camshaft position is shown in a schematic flow diagram.

The method shown can be used to determine the camshaft position, the intake camshaft and / or the exhaust camshaft. Depending on the speed n and the temperature T of the inlet tract or the outlet tract, step 1 using a reference model, the angle or angles φ _{_Peak_Verdacht are} determined, in the vicinity of which or at which an extreme value in the pressure curve is present. The value φ _{_Peak_erdacht} can be determined by _{converting the equation NW Mod} = f * φ + K (nT) to φ and _{inserting the measured value NW Ist} : φ _Peak_Verdacht = (NW _ISt -K (n, T)) / f. The values f and K (n, T) are determined on the basis of the reference model or on the basis of reference measurements on the reference motor. This estimate φ _ _{peak suspicion} is used to search for the extreme value more quickly in the next steps.

In a step 2, the measured values around these extreme points in the pressure curve are now selected in a specific interval, for example +/- 20 degrees crankshaft angle. The pressure curve is repeated with every movement of the corresponding cylinder. There is now the preferred possibility that the measured values are averaged by averaging the pressure curve assigned in the first cylinder and the values of the fourth cylinder of the pressure curve, for example. These averaged values are now stored in a field p-NormArray. _{The local largest or smallest measured value φ Peak_grob is} determined from these values of the p-NormArray field.

In step 3, the extreme value is now interpolated using a mathematical model. A polynomial, in particular a quadratic polynomial, is preferably used for this purpose. The coefficients of the polynomial are determined by a least square estimate. Because the first derivative of the polynomial is formed and set equal to “0”, a more precise value φ _{Peak_fein} can now be determined, which is compared in a step 4 with data from the reference measurement or with a reference model.

By determining the extreme value φ _{Peak_fein of} the series engine, the exact position of the camshaft can now be determined through a comparison with the reference measured values or the reference model of the reference engine. The actual camshaft value NW_mod is determined in step 4 by multiplying the crankshaft _{angle φ Peak_fein of} the extreme with a factor f and adding a correction value, the factor f and the correction value being determined from the reference measured values: $${\text{NW}}_{\text{Mod}}=\text{f}*{\mathrm{\phi }}_{\text{Peak}\_\text{fine}}+\text{c}.$$

The correction value c is preferably determined with a map K (), the map value depending on physical parameters, preferably a crankshaft speed n and a temperature T of the inlet and / or outlet tract: $${\text{NW}}_{\text{Mod}}=\text{f}*{\mathrm{\phi }}_{\text{Peak}\_\text{fine}}+\text{K}\left(\text{n},\text{T}\right)$$

This is now output as the result NW_mod. This correction of the camshaft position allows valve control times to be determined more precisely, with deviations of the series engine from the reference engine being taken into account in a simple manner.

The model _value φ Peak_fein or the model _value φ Peak_fein minus the real actual angle is preferably averaged. For this purpose, these values are fed to a ring memory. If there are enough values in the ring memory and the spread of these values is below a threshold, the result is reliable. The mean value from the ring memory is the system's camshaft error.

List of reference symbols

1

Process step: Determination of a preliminary extreme value φ _{_Peak_Verdacht} = (NW _Ist -K (n, T)) / f

2

_{Process step: Selection of pressure curve measured values} in an interval around the value φ Peak_Verdacht and averaging of several selected intervals, which are assigned to different cylinders, to form an averaged pressure curve field p-NormArray and determination of the crankshaft _{angle φ Peak_grob of} the largest or smallest measured value in the determined pressure curve of the field p-NormArray

3

_{Method step: Interpolating the averaged pressure curve measured values using} a mathematical model, in particular a polynomial of the second degree, and determining the maximum φ Peak_fein of the model

4th

Process step: Calculation of the model _{value of the camshaft rotational position NW Mod} = f * φ Peak_fein + K (n, T)

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102015209665 A1 [0005]

Claims (11)

Method for determining the camshaft position of a series motor, said reference measured values are determined at a reference engine, wherein a pressure profile having a plurality of pressure measurement values in the inlet and / or outlet zone is detected the series engine, a camshaft actual value (NW _mod) is determined wherein on the basis of the pressure variation, characterized characterized in that at least one crankshaft angle (φ_Peak) of a local extreme of the measured pressure values of the series engine is determined, _{the actual camshaft value (NW Mod} ) of the series engine being determined as a function of the extreme of the reference engine and the determined crankshaft angle (φ_Peak) of the local extreme of the measured pressure values of the series engine . Procedure according to Claim 1 , characterized in that the actual camshaft value NW_mod is determined by multiplying the crankshaft angle (φ_Peak) of the extreme with a factor f and adding a correction factor NW _Mod = f * (φ_Peak + c, the factor f and the correction factor c being determined from the reference measured values is. Procedure according to Claim 2 , characterized in that the correction value is determined by a map c = K (n, T), the map value having been determined from the reference measured values, the map value depending on a crankshaft speed n and a temperature T of the inlet and / or outlet tract is. Method according to one of the preceding claims, characterized in that the camshaft position is determined on cylinders which are in overrun mode. Method according to one of the preceding claims, characterized in that, in order to determine the extreme, a measured value interval of the pressure curve around a crankshaft angle is selected at which the extreme value occurs in the reference model. Method according to one of the preceding claims, characterized in that an averaged measured value interval is formed from several measured value intervals, the measured value intervals being assigned to different cylinders. Method according to one of the preceding claims, characterized in that the extreme value is determined by means of a mathematical equation through a least square estimate of the measured values or the averaged measured values. Method according to the preceding claim, characterized in that the mathematical equation is a polynomial, in particular a polynomial of the second degree. Method according to one of the preceding claims, characterized in that the crankshaft angle of the extreme value takes place as a function of a temperature of the inlet tract or the outlet tract and a crankshaft drive speed. Method according to one of the preceding claims, characterized in that a mean value of the deviation of the actual camshaft value from the reference value is formed. Method according to one of the preceding claims, characterized in that the pressure run of a constant crankshaft speed is determined.

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